Process for the preparation of alcohols

ABSTRACT

Aldehydes, ketones, esters and lactones may be reduced using a reductant system consisting of polymethylhydroxysilane (PMHS) and a metal hydride to give good yields of the corresponding alcohols. The reductant system used in the method enables preferential reduction of the carbonyl function.

This application is a 371 of PCT/IB95/00836 filed Oct. 6, 1995.

TECHNICAL FIELD AND PRIOR ART

The reduction of carbonyl compounds such as aldehydes, ketones, estersor lactones is a choice reaction for the general preparation ofalcohols. In this context, the reduction of the carbonyl function in thecompounds having other unsaturated groups in the molecule, such asethylenic or acetylenic carbon-carbon functions, presents somedifficulties due to the generally poor selectivity of catalytichydrogenation methods via hydrogen. The same applies to the reduction ofcarbonyl compounds having a defined spatial configuration. In fact, theuse of ordinary catalysts such as copperchromites, which only operate atelevated temperatures and pressures, leads to the reduction of the otherfunctionalities present and in many cases, to a modification of thestereochemistry.

In the case of the reduction of unsaturated carbonyl compounds, onlylithium aluminium hydride has the property of reducing at oncealdehydes, ketones and esters in smooth reaction conditions, while beinginert towards unsaturated carbon-carbon bonds eventually present in themolecule. Sodium borohydride or NaAlH₂ (OCH₂ CH₂ OCH₃)₂, Vitride®!, alsoused to promote the carbonyl function reduction, are weakly reactivetowards esters. All these reagents, the use of which requiresstoechiometric amounts, show the major drawback of being sensitive tomoisture and air; furthermore, these reagents are very costly andpollutant, leading to the necessity of developping more economical andeasier to handle systems.

It is noteworthy that the polymethyl-hydroxysilane (PMHS), which isdefined by the following general formula:

    (CH.sub.3).sub.3 --SiO(CH.sub.3 HSiO).sub.n Si(CH.sub.3).sub.3

n being an integer indicating the number of repeated units, can promotethe reduction of aldehydes to alcohols when in the presence of tin basedcatalysts see Nizsche and Wick, Angew. Chem. 1957, 62, 96 and U.S. Pat.No. 3,061,424!.

Grady and Kuivila (J. Org. Chem. 1969, 34, 2014) and Lipowitz and Bowman(Aldrichim. Acta 1973, 6, 1 and J. Org. Chem. 1975, 33, 162) have shownthat, for the reducing system PMHS, the tin catalysis could be appliedto the reduction of aldehydes and ketones, but not to that of estersinto alcohols.

U.S. Pat. No. 5,220,020 describes a method for the preparation ofalcohols by reduction of carbonyl compounds by means of a systemconstituted by a silanic reducing agent and a metal catalyst of formula

    M(L)(L')(L") to M(L)(L')(L")(L'")(L'.sup.v)(L.sup.v)

wherein M is a metal belonging to group 3, 4, 5 or 6, a lanthanide or anactinide, whereas (L') to (L^(v)) represent hydrogen, an alkyl, an aryl,a silyl, a halogen, or a radical --OR, --SR or --N R(R'), wherein R andR' are hydrogen, an alkyl or an aryl. Such a system could be applied tothe reduction of esters, lactones, amides and imides.

Among the preferred catalysts, the patent above-cited mentions titane(IV) isopropylate and ethylate, as well as trichlorotitane (IV)isopropylate.

More recently Barr, Berk and Buchwald (J. Org. Chem. 1994, 59, 4323)have shown that the complex Cp₂ TiCl₂ reduced by butyllithium orethylmagnesium bromide could catalyse the reduction of esters to thecorresponding alcohols with good yields, but this technique requiresexpensive catalytic reagents, which are difficult to use on a largescale in the context of an industrial preparation.

DESCRIPTION OF THE INVENTION

We have now discovered that it was possible to prepare alcohols in goodyields and in an economical way, by reduction of carbonyl derivativessuch as aldehydes, ketones, esters and lactones, by means ofpolymethylhydroxysiloxane hydride, in the presence of a catalyst whichcan be prepared in situ or separately, from a metallic salt or complexand a reducing agent.

The process of the invention presents the advantage of employinginexpensive reagents, the use of which requires no particularprecautions regarding protection against moisture or air. We have alsoascertained that the reducing system of the invention does not lead toagglomeration or caking of the reaction medium, as opposed to what wewere able to observe with the prior art systems.

The object of the present invention is therefore a process for thepreparation of alcohols by reduction of the carbonyl function insubstrates belonging to the class of aldehydes, ketones, esters orlactones, which may or may not contain unsaturated functions other thanthe carbonyl group, which is characterized in that:

a. the carbonylated substrate is reacted with stoechiometric amounts ofa silanic agent in the presence of a catalyst prepared from a metallicsalt or complex and a reducing agent,

b. the obtained siloxane is hydrolysed by means of a basic agent, and

c. the desired alcohol thus formed is separated and purified.

The reaction which characterizes the process of the invention isillustrated by the following schemes: ##STR1## for aldehydes andketones, and ##STR2## for esters and lactones.

PREFERRED EMBODIMENT OF THE INVENTION

Trialkylsilanes, dialkylsilanes, trialkoxysilanes orpolymethylhydroxysilane (PMHS) can be used as the silanic agent.

Thus, dimethylsilane, diethylsilane, trimethoxysilane, triethoxysilaneor PMHS will be preferably used. The latter silanic derivative ispreferably used owing to its efficiency and availability.

The catalyst according to the invention can be obtained in situ, in thereaction medium or be prepared separately from a metallic salt orcomplex of general formula MX_(n), wherein M represents a transitionmetal selected amongst zinc, cadmium, manganese, cobalt, iron, copper,nickel, ruthenium and palladium, X an anion such as a halide, acarboxylate or any anionic ligand, and n a number comprised between 1and 4. To this end, there can be used a chloride, bromide, iodide,carbonate, isocyanate, cyanide, sulfate, phosphate, acetate, propionate,2-ethylhexanoate, stearate or naphthenate of one of the above-mentionedmetals, which will be reacted with a reducing agent such as a hydride,in order to generate the active catalyst according to the process of theinvention.

For this purpose, an alkaline hydride such as lithium, sodium orpotassium hydride, or an alkaline earth hydride such as magnesium orcalcium hydride will be used. A boron hydride such as BH₃, a metallicborohydride M⁺ BH₄ (M⁺ Li, Na, K) or M(BH₄)₂ (M=Mg, Zn, Ca), analkylborane R_(n) BH.sub.(4-n) M (R=alkyl, n=1 to 3, M=alkaline metal),an alkoxyborane (RO)_(n) BH.sub.(4-n) M (R=alkyl, n=1 to 3, M=alkalinemetal), an aluminium hydride AlH₃, AlH_(n) R_(3-n) (R=alkyl), MAlH₄(M=Li, Na, K), MAlH_(n) (OR)_(4-n) (M=Li, Na, K), an organic magnesiumcompound of formula RMgX (R=alkyl, X=Cl, Br, I), an organic lithiumcompound RLi (R=alkyl, for example C₁ to C₄ or aryl), can also be used.

We observed that it could be advantageous, especially when the catalystis prepared ex situ, to add to the catalytic system consisting ofmetallic salt and reducing agent a ligand able to complex the formedmetallic hydride and, therefore, to better solubilize said hydride inthe organic phase. As the ligand, an alcohol ether such asmethoxyethanol, or an alcohol amine such as dimethylaminomethanol,diethanolamine or triethanolamine, can be used.

According to a particular embodiment of the invention, a stable andhomogeneous catalytic solution can for instance be formed by reacting,in an inert organic solvent, for example toluene, tetrahydrofuran orisopropyl ether, one equivalent of zinc 2-ethylhexanoate with twoequivalents of Vitride® and one equivalent of dimethylaminoethanol. Thereaction is characterized by hydrogen release. Once this release isfinished, a homogeneous concentrated solution is obtained, which can bestocked for use in the process of the invention.

The concentration of the metallic salt+reducing agent! system, expressedin molar % of metal relative to the substrate, is generally comprisedbetween 0.1 and 10%, preferably between 1 and 5%.

On the other hand, the molar ratio of the reducing agent relative to themetal is generally comprised between about 1 and 2.

When the catalytic system is prepared in situ, the chosen metallicderivative will be reacted with the reducing agent, in an appropriatesolvent. After complete release of the formed hydrogen, the carbonylatedsubstrate to be reduced will be introduced and the silanic agent addedinto the solution.

The typical consumption for example of PMHS will be of 2 equivalents forthe reduction of esters or lactones and of 1 equivalent for reduction ofaldehydes or ketones. The alcohol obtained as the product of thereduction can be separated by hydrolysis of the obtained siloxane, whichhydrolysis can be accomplished by reacting the reaction medium with anaqueous or alcoholic solution of a basic agent, such as for examplecaustic soda (sodium hydroxide), potash (potassium hydroxide), lime(calcium oxide) or sodium carbonate. The proportion of base relative tothe PMHS is comprised between 1 and 2 molar equivalents. Once thehydrolysis is complete, formation of two phases is generally observed.The desired alcohol being in the organic phase, it can be obtained bysimple evaporation of the solvent, with the possibility of submittingthe residue obtained to a distillation for subsequent purification.

As indicated above, one of the advantages of the process of theinvention is that it does not lead to any caking, and that it ispossible to operate without solvent in a very concentrated solution.However, in order to better control the reaction temperature(exothermic), we prefer to operate with a solvent.

As appropriate solvent, an ether such as methyltertbutylether,diisopropylether, dioxane, tetrahydrofuran, ethyleneglycoldimethylethercan be used. An aliphatic hydrocarbon such as heptane, petroleum ether,octane, cyclohexane, or aromatic as benzene, toluene, xylene ormesitylene, can also be used.

As indicated above, the process of the invention allows the reduction ofvarious carbonylated compounds, having or not unsaturations other thanthe carbonyl, for example olefinic, acetylenic functions or nitrilegroups, which groups are not, or are little affected by the reduction.

As example of aldehydic substrates, butanal, pentanal, hexanal,heptanal, octanal, decanal, dodecanal, either in linear or branchedform, can be cited. Other unsaturated aldehydes susceptible of beingreduced into corresponding unsaturated alcohols are acroleine,methacroleine, crotonaldehyde, prenal, citral, retinal, campholenicaldehyde, cinnamic aldehyde, hexylcinnamic aldehyde, formyl pinane andnopal. The aromatic aldehydes such as benzaldehyde, cuminic aldehyde,vanilline, salicylic aldehyde, are also easily reduced into thecorresponding alcohols.

As examples of saturated or unsaturated ketones susceptible of beingreduced by the silanic reducing agents in the process according to theinvention, there can be cited, in a non-limiting manner, hexan-2-one,octan-2-one, nonan-4-one, dodecan-2-one, methyl vinyl ketone, mesityloxyde, acetophenone, cyclopentanone, cyclohexanone, cyclododecanone,cyclohex-1-en-3-one, isophorone, oxophorone, carvone and camphor.

As non-restrictive examples of esters and lactones susceptible of beingreduced by silanic agents according to the process of invention,acetates, propionates, butyrates, isobutyrates, alkyl or aryl benzoates,acrylates, alkyl or aryl crotonates, alkyl cinnamates, methylcis-3-hexenoate, methyl sorbate, methyl salicylate, methyl10-undecylenate, methyl oleate, methyl linoleate, methyl linolenate orany mixture of natural fatty acid esters, caprolactone, butyrolactone,dodecalactone, diketene and sclareolide can be cited.

Esters able to be reduced according to the process of the invention alsoinclude the triglycerides of fatty acids, such as those which constitutethe vegetable or animal oils. When a mixed triglyceride derived fromdistinct fatty acids is reduced, the corresponding saturated orunsaturated alcohols can thus also be obtained simultaneously, accordingto the following reaction scheme: ##STR3##

The substituents R¹, R², and R³ are generally identical or differenthydrocarbon rests which can contain 1 to 20 carbon atoms. When theserests present some ethylenic unsaturations of defined configuration, theresulting alcohols will preserve the same stereochemistry. Thus, oilsrich in linoleic and linolenic acid, such as linseed oils, will beconverted to a mixture enriched in linoleic and linolenic alcohols,whereas the conventional hydrogenolysis of vegetable oils by gaseoushydrogen at high temperature and pressure in the presence of catalystswill be translated into a modification of the double bondsstereochemistry and position in the corresponding alcohols.

Trioleine, peanut oil, sunflower oil, soya oil, olive oil, colza oil,sesame oil, linseed oil, cotton oil, copra oil, grape seeds oil, coconutoil and palm oil, for example, are used as triglycerides which can bereduced by the process of the invention.

The temperature of the reaction is variable and comprised between 0° C.and 150° C., according to the reactivity of the substrate. Moregenerally, we operate between about 50° C. and 110° C.

The invention is illustrated by the following examples, wherein thetemperatures are indicated in degrees centigrade, the yields in molar %,and the abbreviations have the usual meaning in the art.

Reduction of aldehydes

EXAMPLE 1

Reduction of trans-hexen-2-al-1 ##STR4## A three-neck flask of 1 l wascharged with 50 g of isopropyl ether, 1.5 g of solid sodium borohydride(0.04 mole), then 11.3 g of zinc 2-ethylhexanoate (0.04 mole) and themixture was stirred for 15 minutes until the hydrogen release stops.Then 196 g (2 mole) of trans hex-2-en-1-al are introduced, and thereaction is taken to reflux. 147 g of PMHS (2.3 mole) are thenintroduced in 2 h. The reaction is stirred for 2 additional hours untilthe GC control indicates that all the substrate has disappeared. Themixture is then cooled to 20°, 100 g of water are added, then slowly 460g of a 30% aqueous sodium hydroxide, without letting the temperature ofthe reaction mixture increase above 40°.

The mixture is decanted, the aqueous phase containing the sodiumsilicate is separated, then the organic phase is washed with 100 ml ofwater saturated with salt, then with 50 g of a 30% aqueous solution ofacetic acid. The solvent is evaporated and 211 g of residue areobtained, which residue gives by distillation 188 g of transhex-2-en-1-ol with a purity above 95%.

EXAMPLES 2 TO 13

These examples are intended to illustrate the influence of the catalyticsystem and of the solvent over the reduction of trans hex-2-en-1-al totrans hex-3-en-1-ol by the PMHS. We proceed as described in example 1,but with 10 times lower amounts. The solvent, the zinc salt (2% molarrelative to the substrate), the reducing agent (2% molar), then thetrans hex-2-en-1-al are charged. Then 1.1 equivalent of PMHS is added tothe mixture in 1 h and reflux maintained until total consumption of thesubstrate. Hydrolysis with 30% sodium hydroxide is then carried out,then the alcohol formed is recovered as in example 1. It has beenascertained that most of the zinc salts used (ZnCl₂,Zn(2-ethyl-hexanoate)₂, ZnBr₂, ZnEt₂) in combination with a reducingagent (LiH, NaH, NaBH₄, LiAlH₄, Vitride®) are active in the reduction ofhex-2-en-1-al. In no case did we observe isomerisation of the alcoholformed, nor the formation of secondary products.

    ______________________________________                                        Ex-                      Reducing                                                                             Reac-                                         am-            Zinc salt agent  tion  Yield (%) in                            ples Solvent   2% molar  2% molar                                                                             time  hex-3-en-1-ol                           ______________________________________                                        2    methyl tert-                                                                            ZnCl.sub.2                                                                              NaBH.sub.4                                                                           5 h   91%                                          butyl ether                                                              3    isopropyl ZnCl.sub.2                                                                              NaBH.sub.4                                                                           4 h   94%                                          ether                                                                    4    isopropyl Zn(2-ethyl-                                                                             NaBH.sub.4                                                                           5 h   90%                                          ether     hexanoate).sub.2                                               5    isopropyl Zn(2-ethyl-                                                                             LiH    6 h   90%                                          ether     hexanoate).sub.2                                               6    isopropyl Zn(2-ethyl-                                                                             NaH    6 h   78%                                          ether     hexanoate).sub.2                                               7    toluene   Zn(2-ethyl-                                                                             NaBH.sub.4                                                                           4 h   88%                                                    hexanoate).sub.2                                               8    tetrahydro-                                                                             Zn(2-ethyl-                                                                             NaBH.sub.4                                                                           5 h   87%                                          furan     hexanoate).sub.2                                               9    isopropyl ZnBr.sub.2                                                                              NaBH.sub.4                                                                           6 h   77%                                          ether                                                                    10   isopropyl Zn(2-ethyl-                                                                             LiAlH.sub.4                                                                          4 h   90%                                          ether     hexanoate).sub.2                                               11   isopropyl Zn(2-ethyl-                                                                             LiAlH.sub.4                                                                          4 h   89%                                          ether     hexanoate).sub.2                                               12   isopropyl Zn(2-ethyl-                                                                             Vitride ®                                                                        6 h   87%                                          ether     hexanoate).sub.2                                                                        .sup.1)                                              13   toluene   ZnEt.sub.2                                                                              LiAlH.sub.4                                                                          5 h   85%                                     ______________________________________                                         .sup.1) Vitride ® = NaAlH.sub.2 (OCH.sub.2 CH.sub.2 OMe).sub.2       

EXAMPLES 14 TO 27

These examples illustrate the possibility to selectively reduce numerousaldehydes to the corresponding alcohols, without modification of thestarting molecule's stereochemistry.

Proceeding as described in example 1, 10 ml of isopropyl ether arecharged in the reactor, then 4 mmole of zinc 2-ethyl-hexanoate, then 4mmole of NaBH4, and finally 0.2 mole of the substrate to be reduced.0.22 mole of PMHS are then introduced in 1 h under reflux of thesolvent. When the substrate has disappeared, hydrolysis of the reactionmedium is carried out with 30% aqueous sodium hydroxide, and the alcoholformed is isolated as in example 1.

    __________________________________________________________________________    Exam-                                                 Reaction                                                                            Yield             ples                                                                             Substrate                Product                   time  (%)               __________________________________________________________________________    14                                                                                ##STR5##                                                                                               ##STR6##                 3 h   93%               15                                                                                ##STR7##                                                                                               ##STR8##                 4 h   90%               16                                                                                ##STR9##                                                                                               ##STR10##                4 h   95%               17                                                                                ##STR11##                                                                                              ##STR12##                6 h   87%               18                                                                                ##STR13##                                                                                              ##STR14##                5 h   95%               19                                                                                ##STR15##                                                                                              ##STR16##                4 h   90%               20                                                                                ##STR17##                                                                                              ##STR18##                3 h   94%               21                                                                                ##STR19##                                                                                              ##STR20##                4 h   90%               22                                                                                ##STR21##                                                                                              ##STR22##                3 h   96%               23                                                                                ##STR23##                                                                                              ##STR24##                5 h   80%               24                                                                                ##STR25##                                                                                              ##STR26##                4 h   91%               25                                                                                ##STR27##                                                                                              ##STR28##                5 h   89%               26                                                                                ##STR29##                                                                                              ##STR30##                4 h   92%               27                                                                                ##STR31##                                                                                              ##STR32##                3                       __________________________________________________________________________                                                                h   97%                                                                       2                  .sup.1) The citral used is a 50-50 mixture of geranial and neral         

Reduction of ketones

EXAMPLE 28 ##STR33## In a three-neck flask of 1 l, 50 g of isopropylether, 5 g of LiAlH₄ in a 15% toluene solution (0.01 mole), then 1.36 gof zinc chloride (0.01 mole) are introduced and stirred for 15 minutesuntil the hydrogen release stops. Then, 110 g (0.5 mole) of3,3-dimethyl-5-(2,2,3-trimethyl-cyclopent-3-en-1-yl)-pent-4-en-2-one(formula 1 above) are introduced, and the reaction medium is taken toreflux. Then 36 g of PMHS (0.55 mole) are introduced in 1 h. Thereaction is stirred for 2 additional hours until the GC controlindicates that all the substrate had disappeared. The mixture is thencooled to 20°, then 85 g of 45% aqueous potassium hydroxide are addedslowly, without letting the temperature of the reaction increase above40°, and the reaction is kept under stirring for 1 h.

The mixture is decanted, the aqueous phase containing the sodiumsilicate is separated, then the organic phase is washed with 100 ml ofwater. The solvent is evaporated and 116 g of product are obtained, thedistillation of which on residues gives 105 g of3,3-dimethyl-5-(2,2,3-trimethyl-cyclopent-3-en-1-yl)-pent-4-en-2-ol(formula 2 above) of purity higher than 98% (yield=95% molar).

EXAMPLES 29 TO 37

A 250 ml three-neck flask is charged with 50 ml of isopropyl ether, then0.4 g of solid sodium borohydride (10 mmole), and 10 mmole of metallicsalt or complex, the nature of which is indicated in the table. Themixture is allowed to react for 30 minutes at reflux until the hydrogenrelease stops, then 50 g of cyclohex-1-en-3-one (0.57 mole) areintroduced. 37.2 G of PMHS (0.57 mole) are then introduced in thereaction mixture in 30 minutes and the progress of the reaction iscontroled by GC. Hydrolysis of the reaction medium is carried out with100 g of 30% weight aqueous caustic sodium hydroxide, and the product orproducts formed are recovered by distillation as in the previousexamples.

    __________________________________________________________________________                               Cyclohex-1-                                                                         Cyclohex-                                                Reducing       en-3-ol                                                                             anone (%)                                         metallic salt                                                                        agent                                                                              Time                                                                              Conversion                                                                          Selectivity                                                                         Selectivity                                  Examples                                                                           2% molar                                                                             2% molar                                                                           (hours)                                                                           (%)   (%)   (%)                                          __________________________________________________________________________    29   Mn(2-ethyl-                                                                          NaBH.sub.4                                                                         5   95    100   0                                                 hexanoate).sub.2                                                         30   Co(2-ethyl-                                                                          NaBH.sub.4                                                                         6   97    98    0                                                 hexanoate).sub.2                                                         31   Fe(2-ethyl-                                                                          NaBH.sub.4                                                                         8   99    98    0                                                 hexanoate).sub.2                                                         32   CdCl.sub.2                                                                           NaBH.sub.4                                                                         5   24    98    2                                            33   Cu(2-ethyl-                                                                          NaBH.sub.4                                                                         20  45    1     99                                                hexanoate).sub.2                                                         34   Ni(2-ethyl-                                                                          NaBH.sub.4                                                                         15  96    13    87                                                hexanoate).sub.2                                                         35   PdCl.sub.2 (PPh.sub.3).sub.2                                                         NaBH.sub.4                                                                         3   99    21    79                                           36   RuCl.sub.2 (PPh.sub.3).sub.3                                                         NaBH.sub.4                                                                         2   92    46    54                                           37   Cr(2-ethyl-                                                                          NaBH.sub.4                                                                         14  38    74    22                                                hexanoate).sub.2                                                         __________________________________________________________________________

EXAMPLES 38 TO 47

We proceeded as described in example 28, operating in isopropyl ether atreflux (68°), but using as catalyst a mixture of 2% molar zinc2-ethylhexanoate, relative to the substrate, and 2% molar of NaBH₄. 0.5Mole of ketonic substrate are used, which are reduced by 0.55 mole ofPMHS. When the substrate has disappeared, the hydrolysis is thenaccomplished with 0.7 mole of 45% aqueous potassium hydroxide. Afterdecantating and evaporation of the solvent, the distillation of theformed alcohol is carried out. The results of the tests indicated in thetable show that in all the cases the reduction is accomplished veryselectively and with excellent yields, without modification of thestarting molecule's stereochemistry.

    __________________________________________________________________________                                                 Reaction                         Examples                                                                           Substrate           Product             time Yield(%)                    __________________________________________________________________________    38                                                                                  ##STR34##                                                                                         ##STR35##          3 h  97%                         39                                                                                  ##STR36##                                                                                         ##STR37##          4 h  95%                         40                                                                                  ##STR38##                                                                                         ##STR39##          4 h  95%                         41                                                                                  ##STR40##                                                                                         ##STR41##          4 h  94%                         42                                                                                  ##STR42##                                                                                         ##STR43##          3 h  92%                         43                                                                                  ##STR44##                                                                                         ##STR45##          3 h  97%                         44                                                                                  ##STR46##                                                                                         ##STR47##          4 h  94%                         45                                                                                  ##STR48##                                                                                         ##STR49##          4 h  96%                         46                                                                                  ##STR50##                                                                                         ##STR51##          5 h  95%                         47                                                                                  ##STR52##                                                                                         ##STR53##          4 h  90%                         __________________________________________________________________________

Reduction of esters and lactones

EXAMPLE 48 ##STR54## 50 G of isopropyl ether, 0.7 g of NaBH₄ (0.018mole), then 1.26 g of zinc 2-ethyl-hexanoate (0.018 mole) are introducedin a 1 l three-neck flask and stirred for 15 minutes until the hydrogenrelease stops. Then, 120 g (0.6 mole) of methyl 10-undecylenate areadded, and the reaction medium is taken to reflux. Then 90 g of PMHS(1.38 mole) are introduced in 1 h. The reaction is stirred for 2additional hours under reflux at 68° until the GC control indicates thatall the substrate has disappeared. The mixture is cooled to 20°, then300 g of 30% methanolic potassium hydroxide are added slowly undervigourous stirring, and stirring is kept for 1 h.

600 Ml of water are then added, and the mixture is decanted. The aqueousphase containing the sodium silicate is separated, then the organicphase is washed with 100 ml of water. The solvent is evaporated and 104g of product is obtained, the distillation of which on residues gives 96g of 10-undecenol with a purity above 98% (yield=94% molar).

EXAMPLES 49 TO 61

Operating in isopropyl ether at reflux (68°), we proceed as described inexample 48, using as catalyst a mixture of 2% molar of zinc2-ethyl-hexanoate relative to the substrate and 2% molar of NaBH₄. 0.5Mole of ester or lactone are used and reduced by 1.2 mole of PMHS. Whenthe substrate has disappeared, hydrolysis is then accomplished with 1.7mole of 45% alcoholic potassium hydroxide. After decantating andevaporation of the solvent, the distillation of the formed alcohol iscarried out. The results of the tests in the table indicate that in allthe cases the reduction of the esters and lactones is accomplished veryselectively and with excellent yields, without modification of thestarting molecule's stereochemistry.

    __________________________________________________________________________                                                           Reaction                                                                           Yield             Examples                                                                            Substrate                 Product                time (%)               __________________________________________________________________________    49                                                                                   ##STR55##                                                                                               ##STR56##             3 h  97%               50                                                                                   ##STR57##                                                                                               ##STR58##             4 h  95%               51                                                                                   ##STR59##                                                                                               ##STR60##             5 h  90%               52                                                                                   ##STR61##                                                                                               ##STR62##             8 h  70%               53                                                                                   ##STR63##                                                                                               ##STR64##             5 h  85%               54                                                                                   ##STR65##                                                                                               ##STR66##             4 h  95%               55                                                                                   ##STR67##                                                                                               ##STR68##             5 h  95%               56                                                                                   ##STR69##                                                                                               ##STR70##             4 h  90%               57                                                                                   ##STR71##                                                                                               ##STR72##             6 h  94%               58                                                                                   ##STR73##                                                                                               ##STR74##             5 h  65%               59                                                                                   ##STR75##                                                                                               ##STR76##             5 h  60%               60                                                                                   ##STR77##                                                                                               ##STR78##             3 h  93%               61                                                                                   ##STR79##                HOCH.sub.2 (CH.sub.2).sub.13 CH.sub.2                                                                5                      __________________________________________________________________________                                                                h  86%                                                                        1             

Triglycerides reduction

EXAMPLE 62

In a three-neck flask of 1 l, 400 g of toluene are introduced, then 1.2g of sodium borohydride and 11 g of zinc 2-ethylhexanoate. The mixtureis heated to 80° C. during about 30 min, until the hydrogen releasestops. Then 200 g of trioleine (glycerol trioleate) are introduced,followed, in 2 hours, by 130 g of PMHS, while keeping the solution at110° C., the reflux temperature of toluene. The reaction is stirred for4 additional hours, until the GC analysis of the samples hydrolysed with30% methanolic potassium hydroxide indicates that the quantity of oleicalcohol formed no longer increases.

The reaction mixture is then poured over 450 g of a 30% methanolicpotassium hydroxide solution, keeping the temperature below 40° C., andthe reaction is allowed to proceed for 1 additional hour. Then 400 ml ofwater are added to the solution and the latter is allowed to decant. Theorganic phase is then separated and the toluene is evaporated. 185 G ofa product consisting of oleic alcohol (Z-9-octadecen-1-ol) having apurity of 96% are then distilled under high vacuum (1 mm Hg) at200°-250° C.

EXAMPLE 63

We proceed as in example 62, but using 200 g of peanut oil. 120 G of amixture consisting of 14% of 1-hexadecanol, 55% of oleic alcohol and 17%of linoleic alcohol (Z,Z-9,12-octadecadien-1-ol) are obtained bydistillation.

EXAMPLE 64

We proceed as in example 62, but using 200 g of sunflower oil. 110 G ofa mixture formed of 12% of 1-hexadecanol, 35% of oleic alcohol and 40%of linoleic alcohol (Z,Z-9,12-octadecadien-1-ol) are obtained bydistillation.

EXAMPLE 65

We proceed as in example 62, but using 200 g of linseed oil. 110 G of amixture formed of 5% of 1-hexadecanol, 18% of oleic alcohol, 17% oflinoleic alcohol (Z,Z-9,12-octadecadien-1-ol) and 52% of linolenicalcohol (Z,Z,Z-9,12,15-octadecatrien-1-ol) are obtained by distillation.

EXAMPLE 66

We proceed as in example 62, but using 200 g of colza oil. 110 G of amixture formed of 58% of oleic alcohol, 20% of linoleic alcohol(Z,Z-9,12-octadecadien-1-ol) and 8% of linolenic alcohol(Z,Z,Z-9,12,15-octadecatrien-1-ol) are obtained by distillation.

I claim:
 1. Process for the preparation of alcohols by reduction of thecarbonyl function in substrates belonging to the class of aldehydes,ketones, esters or lactones, optionally containing unsaturated functionsother than the carbonyl group, which process comprises:a. reacting thecarbonylated substrate with stoichiometric amounts ofpolymethylhydroxysilane (PMHS) in the presence of a catalytic systemprepared from(i) a metallic salt or complex having the formula MX_(n),wherein M represents a transition metal selected from the groupconsisting of zinc, cadmium, manganese, cobalt, iron, copper, nickel,ruthenium and palladium, X an anion such as a halide, a carboxylate orany anionic ligand, and n a number from 1 to 4, and (ii) a reducingagent selected from the group consisting of lithium hydride, sodiumhydride, potassium hydride, an alkaline earth metal hydride, a boronhydride, a metallic borohydride, an alkylborane, an alkoxyborane, analuminum hydride, an organic magnesium compound and an organic lithiumcompound, to form a siloxane b. hydrolyzing the siloxane by means of abasic agent, and c. separating and purifying the desired alcohol thusformed.
 2. Process according to claim 1, wherein the concentration ofsaid catalytic system, expressed in molar percent of metal relative tothe substrate, is between 0.1 and 10%.
 3. Process according to claim 1,wherein the hydrolysis of the siloxane is carried out with caustic soda,potash, lime or sodium carbonate as the basic agent.
 4. Processaccording to claim 1, wherein the reaction is carried out in an inertorganic solvent selected from the group consisting of the ethers and thealiphatic or aromatic hydrocarbons.
 5. Process according to claim 1,wherein the reaction is carried out at a temperature of between about50° and 110° C.
 6. Process according to claim 1, wherein3-methyl-cyclopenta-1,5-dione is reduced to provide3-methyl-cyclopenta-dec-4(5)-en-1-one.
 7. Process according to claim 1,wherein3,3-dimethyl-5-(2,2,3-trimethyl-cyclopent-3-en-1-yl)-pent-4-en-2-one isreduced to provide3,3-dimethyl-5-(2,2,3-trimethyl-cyclopent-3-en-1-yl)-pent-4-en-2-ol. 8.Process according to claim 1, wherein trans-hex-2-en-1-al is reduced toprovide trans-hex-2-en-1-ol.
 9. Process according to claim 1, wherein atriglyceride of a fatty acid of formula ##STR80## wherein R¹, R², and R³represent identical or different hydrocarbon rests, saturated orunsaturated, containing 1 to 20 carbon atoms, is reduced to form thecorresponding alcohols of formula R¹ CH₂ OH, R² CH₂ OH and R³ CH₂ OH.10. Process according to claim 9, wherein a vegetable oil is used as thetriglyceride of a fatty acid.
 11. Process according to claim 10, whereinthe vegetable oil is selected from the group consisting of trioleine,peanut oil, sunflower oil, soya oil, olive oil, colza oil, sesame oil,linseed oil, cotton oil, copra oil, grape seeds oil, coconut oil andpalm oil.
 12. Process according to claim 1, wherein the catalytic systemis formed in-situ in the reaction medium or ex-situ from the reactionmedium.
 13. Process according to claim 12, wherein the transition metalis zinc, manganese, cobalt or iron.
 14. Process according to claim 12,wherein the anion X is chosen from the group consisting of chloride,bromide, iodide, carbonate, isocyanate, cyanate, sulfate, phosphate,acetate, propionate, 2-ethylhexanoate, stearate and naphthenate. 15.Process according to claim 12, which comprises adding to the reactionmedium a complexing agent of the formed metallic hydride.
 16. Processaccording to claim 15 wherein the complexing agent is selected from thegroup consisting of ether alcohols and amine alcohols.
 17. Processaccording to claim 12, wherein the reducing agent is sodium borohydride.18. Process according to claim 16 wherein the complexing agent isselected from the group consisting of methoxyethanol,dimethylaminomethanol, dimethylaminoethanol, diethanolamine andtriethanolamine.
 19. A reductive system capable of being mixed togetherto effect reduction of a carbonylated substrate to an alcohol,comprising:a. polymethylhydroxysilane (PMHS); b. a metallic salt orcomplex according to the general formula MX_(n), wherein M represents atransition metal selected from the group consisting of zinc, cadmium,manganese, cobalt, iron, copper, nickel, ruthenium and palladium, X ananion such as a halide, a carboxylate or any anionic ligand, and n anumber from 1 to 4; and c. a reducing agent selected from the groupconsisting of lithium hydride, sodium hydride, potassium hydride, analkaline earth metal hydride, a boron hydride, a metallic borohydride,an alkylborane, an alkoxyborane, an aluminum hydride, an organicmagnesium compound and an organic lithium compound,wherein components(b) and (c), upon being reacted together, form a catalyst which iseffective to catalyze the reduction of said substrate by component (a).20. A catalyst composition comprising the reaction product of a zincsalt or complex and sodium borohydride complexed with a complexingagent.
 21. Composition according to claim 20, wherein the zinc salt orcomplex is Zn(2-ethylhexanoate)₂.
 22. Composition according to claim 20,wherein the complexing agent is selected from the group consisting ofether alcohols and amine alcohols.
 23. Composition according to claim22, wherein the complexing agent is selected from the group consistingof methoxyethanol, dimethylaminomethanol, dimethylaminoethanol,diethanolamine and triethanolamine.
 24. Process according to claim 12,wherein the substrate is an aldehyde selected from the group consistingof linear or branched butanal, pentanal, hexanal, heptanal, octanal,decanal and dodecanal, acrolein, methacrolein, crotonaldehyde, prenal,citral, retinal, campholenic aldehyde, cinnamic aldehyde, hexylcinnamicaldehyde, formyl pinane, nopal, benzaldehyde, cuminic aldehyde,vanilline and salicylic aldehyde.
 25. Process according to claim 12,wherein the substrate is a ketone selected from the group consisting ofhexan-2-one, octan-2-one, nonan4-one, dodecan-2-one, methyl vinylketone, mesityl oxyde, acetophenone, cyclopentanone, cyclohexanone,cyclododecanone, cyclohex-1-en-3-one, isophorone, oxophorone, carvoneand camphor.
 26. Process according to claim 12, wherein the substrate isan ester or a lactone selected from the group consisting of theacetates, propionates, butyrates, isobutyrates, alkyl and arylbenzoates, acrylates, alkyl and aryl crotonates, alkyl cinnamates,methyl cis-3-hexenoate, methyl sorbate, methyl salicylate, methyl10-undecylenate, methyl oleate, methyl linoleate, methyl linolenate, amixture of natural fatty acid esters, caprolactone, butyrolactone,dodecalactone, diketene and sclareolide.
 27. Process according to claim13, wherein the reducing agent is sodium borohydride.
 28. Processaccording to claim 13, wherein the anion X is chosen from the groupconsisting of chloride, bromide, iodide, carbonate, isocyanate, cyanate,sulfate, phosphate, acetate, propionate, 2-ethylhexanoate, stearate andnaphthenate.
 29. Process according to claim 13, which further comprisesadding to the reaction medium a complexing agent of the formed metallichydride.
 30. Process according to claim 29, wherein the complexing agentis selected from the group consisting of ether alcohols and aminealcohols.
 31. Reductive system according to claim 19, wherein theconcentration of said catalyst, expressed in molar percent of metalrelative to said substrate, is between 0.1 and 10%.
 32. Reductive systemaccording to claim 19, wherein PMHS is employed in approximatelystoichiometric amounts relative to said substrate.
 33. Reductive systemaccording to claim 19, wherein said catalyst is provided in a molarratio of reducing agent relative to metal of between about 1 and
 2. 34.Reductive system according to claim 19, wherein the transition metal inthe metallic salt or complex is zinc, manganese, cobalt or iron. 35.Reductive system according to claim 19, wherein the reducing agent issodium borohydride.
 36. Reductive system according to claim 19, whereinthe anion in the metallic salt or complex is selected from the groupconsisting of chloride, bromide, iodide, carbonate, isocyanate, cyanate,sulfate, phosphate, acetate, propionate, 2-ethylhexanoate stearate andnaphthenate.
 37. Reductive system according to claim 19, furthercomprising a complexing agent for the formed metallic hydride that isformed.
 38. Reductive system according to claim 37, wherein thecomplexing agent is selected from the group consisting of ether alcoholsand amine alcohols.
 39. Reductive system according to claim 38, whereinthe complexing agent is methoxyethanol, dimethylaminomethanol,dimethylaminoethanol, diethanolamine or triethanolamine.
 40. Reductivesystem according to claim 34, wherein the metallic salt or complex isZn(2-ethylhexanoate)₂, Co(2-ethylhexanoate)₂ or Mn(2-ethylhexanoate) andthe reducing agent is sodium borohydride.
 41. Catalyst according toclaim 20 wherein the ratio of reducing agent relative to metal isbetween about 1 and
 2. 42. Process according to claim 1 wherein thereaction is carried out at a temperature of between about 0° and 150° C.